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wide bands of bark at b.h. were made from measurements of d.b.h. and total bark thickness of
every tree in each plot. Fine root biomass was determined in soil cores obtained with a post hole
digger (inner diam. 15.3 cm); traditional small core methods could not be used because of the
high gravel and rock content of the soil.
638. Wagner, R.G. and S.R. Radosevich. 1991a. Interspecific competition and other factors
influencing the performance of Douglas-fir saplings in the Oregon Coast Range. Canadian-
Journal-of-Forest-Research 21(6): 829-835.
Keywords: site preparation
prescribed fire
growth
tree morphology
Abstract: Regression models describing total height, stem diameter, stem volume index,
and crown volume index of individual 4- to 9-year-old saplings of Douglas fir (Pseudotsuga
menziesii) were developed from a retrospective analysis of two site preparation experiments
(with/without prescribed burning). Measurements of 787 Douglas fir saplings were taken at nine
sites during July and August 1984. The variables included in the models were age, interspecific
competition index, height, animal damage (browsing and clipping), use of prescribed burning,
and slope angle and azimuth. The models, which integrate environmental and morphological
factors that can influence the performance of Douglas fir saplings into one set of equations,
accounted for 64-73% of the variation in individual tree size. Interspecific competition and
amount of animal damage were negatively correlated with tree size. Tree age, 1st-year height, and
the use of prescribed burning were positively correlated with tree size. When factors were held
constant, trees were largest on steep southeast slopes. The models indicated that tree age,
competing vegetation, animal damage, and initial seedling size had a dominant influence on the
performance of Douglas fir saplings, while prescribed burning and topography were of relatively
minor importance.
639. Wagner, R.G. and S.R. Radosevich. 1991b. Neighborhood predictors of interspecific competition
in young Douglas-fir plantations. Canadian-Journal-of-Forest-Research 21(6): 821-828.
Keywords: site preparation
stand conditions
growth
Abstract: Neighbourhood models describing the effect of interspecific competition on the
height and stem diameter of 4- to 9-year-old saplings of Douglas fir (Pseudotsuga menziesii) were
developed from site preparation experiments in the Oregon Coast Range. Existing study records
and maps were used to randomly select 787 saplings from 78 study plots at nine sites. The
influence of abundance measures, height, distance, and spatial arrangement of nonconiferous
woody plants surrounding individual saplings was examined. Optimum neighbourhood heights
and radii were defined. The best interspecific competition index for predicting Douglas fir height
and stem diameter was total percentage cover for all woody species within a 2.1-m radius. Visual
estimates of neighbour cover were superior to objective measures of crown area. The cover of
woody species equalling or exceeding the height of the tree provided the best prediction for tree
height. Woody species cover equalling or exceeding one-half the height of the tree provided the
best index for predicting stem diameter. Accounting for the spatial arrangement of neighbouring
woody plants did not improve the competition index. Interaction between the competition index
and tree age indicated that the negative effect of interspecific competition on Douglas fir size